1. Field of the Invention
Broadly speaking, this invention relates to text-processing. More particularly, this invention relates to text-processing systems which employ visual presentations of textual matter comprising, for example, words or graphic images, which are composed and edited and/or stored electronically for future recall.
2. Description of the Prior Art
Prior art text-processing systems typically employ a memory for storing a plurality of digital data words, each of said words representing a textual character or a formatting instruction, a central processing unit (CPU) and associated electronics for presenting or displaying selected characters on the face of a cathode ray tube (CRT). The characters and formatting instructions (used to present characters in a predetermined format) are generally entered into the memory of prior art word-processing systems via a keyboard which encodes them, as well as non-displayed characters, e.g. spaces, tabs, etc. in, for example, the standard ASCII format.
Such prior art CRT text-processing systems may employ any of several well known techniques to draw the characters on the screen. For example, the characters may be drawn utilizing contiguous light spot, starburst, raster scan or vector generation techniques. The latter is described, for example, in U.S. Pat. No. 3,660,833, issued May 2, 1972 and entitled System for Producing Characters on a Cathode Ray Tube Display by Intensity Controlled Point-to-Point Vector Generation.
In addition to moving the electron beam to draw a character on the screen (i.e. "minor" positioning), all text-processing systems must also move the beam to adjacent or other selected positions on the screen so that a character may there be drawn (i.e. "major" positioning). In vector generation type systems such major positioning is typically accomplished by moving the beam while sequentially stepping the memory through a series of addresses, during which time the beam is blanked on the screen, until an active address is reached which calls for a character to be drawn.
Regardless of the technique utilized to draw the characters in prior art CRT text-processing systems, the major positioning function is a sequential type of operation. For example, in raster scan systems the beam is moved horizontally across a raster line as it is turned on and off in accordance with instructions stored in the memory. At the end of each raster line the beam is moved vertically downward and then again horizontally to the right. The beam in such raster systems must, of necessity, pass through each character position on a line, regardless of how much of the display is blanked out. Accordingly, much time is wasted in the major positioning of the beam.
Also, in prior art vector systems, as described, for example, in the aforementioned U.S. Pat. No. 3,660,833, major-positioning may be accomplished by incrementally moving the beam between printing positions by means of X and Y position counters. Such systems are relatively inefficient, since a considerable amount of time is required to step the counters, which must be done even if the beam is stepping through blank spaces.
Since the memory of prior art text-processing systems may be stepped at a more rapid rate than the beam, the data is usually ready to be drawn at a particular character location on the screen before the beam reaches the location. Accordingly, such prior art systems necessarily had to incorporate a minimum fixed time delay, on the order of 1 .mu.sec., in order to inhibit data from being written while the beam was being moved from one character position to the adjacent character position. Obviously, the use of X and Y position counters and incremental stepping of the beam-controlling signals produces a plurality of these undesirable 1 .mu.sec. delays. Even if a carriage return (CR) signals is provided at the end of each line of displayed text to instruct the beam to go to the next line, prior art text-processing systems utilize a fixed time delay prior to turning the beams on to assure that the beam was properly placed for drawing. While the time required to move the beam is naturally a function of distance, the delay is constant.
Now, it is well known that a CRT display must be refreshed approximately 60 times per second in order to present a flicker-free image. In prior art systems, the time required to perform the functions of drawing each character, sequentially stepping through each character position, and fetching data and instructions from memory is approximately 1/60 second. This limits prior art systems to simultaneously displaying approximately less than 6600 characters.
In a system limited to 6600 characters, the normal inclusion of word gaps, etc. enables use of a refresh memory having approximately 4096 bits of storage since, generally, not all available CRT locations have displayed characters therein.
The limitations on the number of characters that may be displayed flicker-free by prior art systems is clearly undesirable. Prior art systems generally display characters on a CRT screen in a format such that the screen represents a page of text, the page generally being equivalent to one typed 81/2.times.11 inch sheet of paper. Such prior art systems are accordingly further limited in the amount of information that may be displayed on the screen in that they are unable to present more than one page at a time on the screen.
In addition, prior art word-processing systems typically present the words or characters on the CRT screen in a certain predetermined format, which is not necessarily the same format in which the data is to be ultimately presented. For example, the CRT screen may display unjustified text while the printer associated with the CRT display may be programmed to print justified text. In prior art systems, then, the operator is unable to determine the effect that justification (i.e. altering inter-character spacing to achieve uniform margins) will have on the appearance of the characters on the page. Accordingly, the final printed product often is undesirable and must be redone.
Moreover, prior-art text-processing systems are incapable of automatically presenting footnotes on the CRT screen in conjunction with the assorted text. In the prior art manipulation of footnoted data generally proceeds by the very indirect process of recording the footnote in a separate memory location and recalling it at a time when the footnoted data is required to be printed at the bottom of a page.
Furthermore, prior art systems are incapable of presenting proportionality spaced characters on the CRT screen. Proportional spacing is distinguished from justification in that the former is a means of sensing and adjusting the inter-character spacing as a function of the inherent width of a displayed character. Justification, on the other hand, may be accomplished by stretching or shrinking the inter-character spacing as required, without necessarily having any proportional spacing.
In prior art text-processing systems, underlining of proportional and/or justified text is not presented on the CRT.
In addition, Prior art mono-spaced systems are not easily adaptable to underline text when proportional spacing is employed because of the large number of different lengths of underline "characters" that would have to be stored in order to underline the many variable lengths of text that may be displayed.
Prior art systems are, in addition, incapable of underlining proportional and/or justified text. Prior art systems which are capable of underlining, do so only in a mono-spaced format and often provide a "pseudo" underlining feature by brightening or contrasting that portion of the text displayed on the CRT that is desired to be underlined upon conversion to a printed format.
Also, prior art systems are incapable of providing variable inter-line spacing and are, thus, limited in their ability to present superscripts and subscripts on the CRT display. An additional disadvantage in the lack of a variable inter-line spacing feature is that, in the event a displayed page of text has only one line, such prior art systems would necessarily have to print that page if the text were printed. If variable inter-line spacing is employed, however, that line could be dislayed and printed on the preceding page by merely shrinking each of the inter-line spaces on the preceding page vertically a very small amount, thus saving wasted time and paper.
Additionally, prior art text-processing systems are limited in the number of characters that they may display without utilizing a larger and more expensive memory. This drawback is especially apparent in foreign language applications where certain letters are the same as in English with the exception that one letter may have an accent mark (acute, grave or circumflex as in French, or an umlaut as in German) while the other does not. To represent the extra letters that have accent marks and all of the various combinations of letters and accent marks would necessitate a larger memory. This would obviously increase the cost and complexity of the text processing system. Accordingly, there exists a need to enable a word processing system to perform an overstrike function wherein basic letters may be stored in memory as well as basic accent marks which may then be selectively combined, without increasing memory storage capacity appreciably.
One of the drawback of prior art text processing systems, which limits the number of characters that may be displayed, is that in order to display two pages of text on the screen, the display processing unit of the system must, necessarily, be operated at a faster rate in order to refresh the display a sufficient number of time per second to ensure elimination of flicker. This places great demands on the CPU which, in addition to reading the memory and providing the data which is to be refreshed, must also perform all formatting functions including the reading and interpreting of non-displayed codes such as carriage returns, inter-line spaces, etc.
While prior art devices may, in theory, be re-organized to overcome some of the aforementioned disadvantages, the very high clock rates that would be required to do this would necessarily dictate the use of high clock-rate logic devices, which are more expensive than slower devices, and result in a considerably more complex system.
A further disadvantage to prior art systems is the fact that they are incapable of easily presenting italicized text and altering the size of the displayed characters.
Accordingly, there exists a need for a CRT text-processing system which is capable of overcoming the aforementioned prior art deficiencies without unduly increasing the cost and complexity of the associated hardware.